The paper's lead author Dr John Emmert from the Naval Research Laboratory in Washington DC says levels of carbon dioxide and carbon monoxide have reached 200 parts per million in the thermosphere - 100 kilometres above the Earth's surface - a third more than predicted by atmospheric models.

Current CO2 levels are just below 400 parts per million near ground level.

"We've seen a decrease in satellite drag and the suspected primary culprit for that was CO2 increases," says Emmert.

"This is the first direct evidence we have that CO2 is definitely increasing in the thermosphere, it's pretty straight forward."

CO2's cooling effect

In the lower atmosphere, carbon dioxide acts as an insulating blanket, preventing heat from the surface escaping.